CMOS on hybrid substrate with different crystal orientations using silicon-to-silicon direct wafer bonding

ABSTRACT

A method in which semiconductor-to-semiconductor direct wafer bonding is employed to provide a hybrid substrate having semiconductor layers of different crystallographic orientations that are separated by a conductive interface is provided. Also provided are the hybrid substrate produced by the method as well as using the direct bonding method to provide an integrated semiconductor structure in which various CMOS devices are built upon a surface orientation that enhances device performance.

RELATED APPLICATIONS

This application is related to co-pending and co-assigned U.S. patentapplication Ser. No. 10/250,241, filed Jun. 17, 2003, the entire contentof which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to high-performance metal oxidesemiconductor field effect transistors (MOSFETs) for digital or analogapplications, and more particularly to MOSFETs utilizing carriermobility enhancement from surface orientation.

BACKGROUND OF THE INVENTION

In present semiconductor technology, CMOS devices, such as nFETs orpFETs, are typically fabricated upon semiconductor wafers, such as Si,that have a single crystal orientation. In particular, most of today'ssemiconductor devices are built upon Si having a (100) crystalorientation.

Electrons are known to have a high mobility for a (100) Si surfaceorientation, but holes are known to have high mobility for a (110)surface orientation. That is, hole mobility values on (100) Si areroughly 2x–4x lower than the corresponding electron mobility for thiscrystallographic orientation. To compensate for this discrepancy, pFETsare typically designed with larger widths in order to balance pull-upcurrents against the nFET pull-down currents and achieve uniform circuitswitching. pFETs having larger widths are undesirable since they take upa significant amount of chip area.

On the other hand, hole mobilities on (110) Si are 2x higher than on(100) Si; therefore, pFETs formed on a (110) surface will exhibitsignificantly higher drive currents than pFETs formed on a (100)surface. Unfortunately, electron mobilities on (110) Si surfaces aresignificantly degraded compared to (100) Si surfaces.

As can be deduced from the above discussion, the (110) Si surface isoptimal for pFET devices because of excellent hole mobility, yet such acrystal orientation is completely inappropriate for nFET devices.Instead, the (100) Si surface is optimal for nFET devices since thatcrystal orientation favors electron mobility.

Methods have been described to form planar hybrid substrates withdifferent surface orientations through wafer bonding. In such endeavors,the planar hybrid substrate is obtained mainly throughsemiconductor-to-insulator, or insulator-to-insulator wafer bonding toachieve pFETs and nFETs on their own optimized crystal orientation forhigh performance device manufacture. However, at least one type ofMOSFET (either pFETs or nFETs) is on a semiconductor-on-insulator (SOI),while the other type of MOSFET is either on a bulk semiconductor or anSOI with a thicker SOI film.

Other technology exists wherein both nFETs and pFETs are fabricated onSOI with the same thickness, but with additional processing steps. SOIdevices generally have higher performance than bulk-like devices due toless parasitic capacitance; however, SOI devices have a floating body(i.e., well), whose effect is known to depend on the SOI thickness.Generally, each SOI device is isolated from the other by a shallowtrench isolation (STI) region and the buried oxide (BOX). This prior artstructure is shown, for example, in FIG. 1. To avoid the floating bodyeffect, each SOI device needs it's own body contact. Such a structurewould significantly increase the area of the chip.

On the other hand, the body of MOSFETs fabricated on a bulk siliconsubstrate is connected through well contacts, which usually are deeperthan the STI. Although bulk-devices are isolated from each other by STI,their body contacts can be connected to each other through a common wellcontact; See, for example, FIG. 2.

In view of the above discussion, there is a need for providing astructure having both pFETs and nFETs on a hybrid substrate withdifferent crystal orientations, wherein the pFET and nFET devices areall bulk-like devices, and wherein each device has a body contactthrough the well or substrate.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a method ofintegrating semiconductor devices such that different types of devicesare formed upon a specific crystal orientation of a hybrid substratethat enhances the performance of each type of device.

Another object of the present invention is to provide a method ofintegrating semiconductor devices such that the pFETs are located on a(110) crystallographic plane, while the nFETs are located on a (100)crystallographic plane of a hybrid substrate.

A further object of the present invention is to provide a method ofintegrating semiconductor devices on a hybrid substrate having differentcrystal orientations such that each device is a bulk-like device and islocated on a crystal orientation which enhances the performance of thedevice.

An even further object of the present invention is to provide a methodof integrating semiconductor devices on a hybrid substrate havingdifferent crystal orientations such that each device has its own bodycontact through a well or the substrate.

An additional object of the present invention is to provide a method ofintegrating different CMOS devices onto a hybrid substrate havingdifferent crystallographic surface planes wherein isolation regions areformed between the different types of CMOS devices.

These and other objects and advantages are achieved in the presentinvention by utilizing a method in which semiconductor-to-semiconductor,especially Si-to-Si, direct wafer bonding is employed as one of theprocessing steps. In accordance with the present invention, twosemiconductor wafers or substrates having different crystal orientationsare subjected to a direct wafer bonding process. Following the directwafer bonding, the hybrid substrate thus obtained is subjected topatterning, etching, regrowth of a semiconductor layer, isolationformation and semiconductor device formation.

One aspect of the present invention relates to a hybrid substrate thatcomprises:

a first semiconductor layer having a first crystallographic orientation;and

a second semiconductor layer having a second crystallographicorientation which is different from the first crystallographicorientation, wherein said first and second semiconductor layers areseparated from each other by a conductive interface.

Another aspect of the present invention is directed to a method offabricating the aforementioned hybrid substrate. Specifically, thehybrid substrate is fabricated using a method that comprises:

providing a first semiconductor wafer comprising a first semiconductormaterial having a first crystallographic orientation and a secondsemiconductor wafer comprising a second semiconductor material having asecond crystallographic orientation which is different from the firstcrystallographic orientation; and

bonding the first semiconductor wafer to the second semiconductor wafer,wherein a conductive interface forms between the two wafers.

A further aspect of the present invention relates to an integratedsemiconductor structure that includes:

a hybrid structure comprising a first device region having a firstcrystallographic orientation and a second device region having a secondcrystallographic orientation, said first crystallographic orientation isdifferent from said second crystallographic orientation;

an isolation region separating said first device region from said seconddevice region; and

at least one first semiconductor device located in said first deviceregion and at least one second semiconductor device located in saidsecond device region, wherein said first semiconductor device and saidsecond semiconductor device are both bulk-like devices and both devicescontain a well region that serves as a body contact.

Another aspect of the present invention relates to a method of formingthe integrated semiconductor structure which includes the steps of:

providing a hybrid substrate comprising at least a first semiconductorlayer of a first crystallographic orientation and a second semiconductorlayer of a second crystallographic orientation separated by a conductiveinterface, said first crystallographic orientation is different fromsaid second crystallographic orientation and said first semiconductorlayer lies below said second semiconductor layer;

selectively etching a portion of the hybrid substrate to expose asurface of the first semiconductor layer;

regrowing a semiconductor material on said exposed surface of the firstsemiconductor layer, said semiconductor material having acrystallographic orientation that is the same as the firstcrystallographic orientation;

providing well regions in said second semiconductor layer and saidregrown semiconductor material; and

forming at least one first semiconductor device on said regrownsemiconductor material, while forming at least one second semiconductordevice on said second semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross sectional view)illustrating a prior art structure including MOSFETs on an SOI substratein which a floating body exists.

FIG. 2 is a pictorial representation (through a cross sectional view)illustrating a prior art structure including MOSFETs on a bulk substratein which well contacts are present.

FIG. 3 is a pictorial representation (through a cross sectional view)showing a hybrid substrate of the present invention having differentsurface orientations which is obtained by semiconductor-to-semiconductordirect bonding.

FIGS. 4A–4B are pictorial representations (through cross sectionalviews) showing various approaches for layer transfer to achieve a thintop semiconductor layer of the hybrid substrate shown in FIG. 3.

FIGS. 5A–5E are pictorial representations (through cross sectionalviews) showing the basic processing steps that are employed in thepresent invention using the hybrid substrate of FIG. 3 as the startingsubstrate.

FIGS. 6–11 are pictorial representations (through cross sectional views)showing some bulk CMOS device design strategies on hybrid substrateswith different surface orientations that can be utilized in the presentinvention.

FIGS. 12A–12D are pictorial representations (through cross sectionalviews) showing one approach for providing a strained Si MOSFET of thepresent invention.

FIGS. 13A–13D are pictorial representations (through cross sectionalviews) showing another approach for providing a strained Si MOSFET ofthe present invention.

FIGS. 14A–14D are pictorial representations (through cross sectionalviews) showing still another approach for providing a strained Si MOSFETof the present invention.

FIGS. 15A–15D are pictorial representations (through cross sectionalviews) showing a further approach for providing strained Si nFET andpFET.

FIGS. 16A–16D are pictorial representations (through cross sectionalviews) showing a still further approach for providing strained Si nFETand pFET.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a method of forming CMOS deviceson a hybrid substrate having different crystal orientations usingsemiconductor-to-semiconductor direct bonding, will now be described inmore detail by referring to the drawings that accompany the presentapplication.

FIG. 3 shows an initial hybrid substrate 10 having differentcrystallographic orientations that can be employed in the presentinvention. Specifically, the hybrid substrate 10 includes a first(bottom) semiconductor layer 12 and a second (top) semiconductor layer16 having a bonding interface 14 located therebetween. In accordancewith the present invention, the first semiconductor layer 12 comprises afirst semiconductor material that has a first crystallographicorientation and the second semiconductor layer 16 comprises a secondsemiconductor material that has a second crystallographic orientationwhich differs from the first crystallographic orientation.

The first semiconductor layer 12 of hybrid substrate 10 is comprised ofany semiconductor material including, for example, Si, SiC, SiGe, SiGeC,Ge, GaAs, InAs, InP as well as other III/V or II/VI compoundsemiconductors. Combinations of the aforementioned semiconductormaterials are also contemplated herein. First semiconductor layer 12 maybe strained, unstrained, or a combination of strained and unstrainedlayers can be used. The first semiconductor layer 12 is alsocharacterized as having a first crystallographic orientation which maybe (110), (111), or (100). The first semiconductor layer 12 mayoptionally be formed on top of a handling wafer.

In embodiments in which the first semiconductor layer 12 is a bulkhandle wafer, its thickness is the thickness of a wafer.

The second semiconductor layer 16 is comprised of any semiconductingmaterial which may be the same or different from that of the firstsemiconductor layer 12. Thus, the second semiconductor layer 16 mayinclude, for example, Si, SiC, SiGe, SiGeC, Ge, GaAs, InAs, InP as wellas other III/V or II/VI compound semiconductors. The secondsemiconductor layer 16 may also include combinations of theaforementioned semiconductor materials. Second semiconductor layer 16may also be strained, unstrained or a combination of strained andunstrained layers can be used, e.g., strained Si on relaxed SiGe.

The second semiconductor layer 16 is also characterized as having asecond crystallographic orientation, which is different from the firstcrystallographic orientation. Thus, the crystallographic orientation ofthe second semiconductor layer 16 is (100), (111), or (110) with theproviso that the crystallographic orientation of the secondsemiconductor layer 16 is not the same as the crystallographicorientation of the first semiconductor layer 12.

The thickness of the second semiconductor layer 16 may vary depending onthe initial starting wafer used to form the hybrid substrate 10.Typically, however, the second semiconductor layer 16 has a thicknessfrom about 50 nm to about 200 μm, with a thickness from about 150 nm toabout 2 μm being more highly preferred.

The bonding interface 14 that is present between the first semiconductorlayer 12 and the second semiconductor layer 16 is a conductiveinterface. The interface 14 typically has a thickness from about 10 nmor less. The thickness of the interface 14 is determined by the bondingprocess used and whether the surfaces are treated with a hydrophilic orhydrophobic agent prior to bonding.

The exact crystal orientations of the first semiconductor layer 12 andthe second semiconductor layer 16 may vary depending on the material ofthe semiconductor layer as well as the type of semiconductor device thatwill be subsequently formed thereon. For example, when Si is employed asthe semiconductor material, electron mobility is higher on a (100)surface orientation, and hole mobility is higher on a (110) surfaceorientation. In this case, the (100) Si surface is used as the devicelayer for nFETs, while the (110) Si surface is used as the device layerfor pFETs.

To achieve bulk-like devices on different surface orientations using thehybrid substrate 10 shown, for example in FIG. 3, the interface 14between the first and second semiconductor layers 12, and 16,respectively, is preferred to have good electrical conductivity. Tomaintain high crystal quality of the second semiconductor layer 16, thedefects/charges should be localized near the interface 14 and notmigrate into the second semiconductor layer 16 (especially near thesurface) during the formation of the hybrid substrate 10 and thesubsequent processes.

The hybrid substrate 10 shown in FIG. 3 is formed in the presentinvention through semiconductor-to-semiconductor direct bonding. In sucha process, two semiconductor substrates or wafers are directly bondedtogether without the presence of an insulating layer therebetween.

Silicon wafer bonding to obtain insulating layers between wafers toachieve semiconductor-on-insulator structure have been widely known andis described, for example, by J. B. Lasky, “Wafer bonding forsilicon-on-insulator technologies”, Appl. Phys. Lett., V 48, p 78(1986); and J. B. Lasky, “Silicon-On-Insulator (SOI) by bonding andetch-back”, IEDM Tech. Dig, p 684, 1985.

The semiconductor-to-semiconductor direct bonding step that is used inthe present invention to obtain a conductive interface 14 between thetwo semiconductor wafers will be described in detail below. The twowafers used in fabricating the hybrid substrate 10 may include two bulksemiconductor wafers; a bulk semiconductor wafer and a wafer containingan etch stop layer 18 and a handling wafer 20 (See FIG. 4A), or a firstbulk wafer and a second bulk wafer which includes an ion implant region22, such as a hydrogen implant (i.e., H₂) region, which can be used tosplit a portion of at least one of the wafers during bonding (See FIG.4B).

In some embodiments of the present invention the bonding processdescribed in U.S. Ser. No. 10/250,241, the entire content of which isincorporated herein by reference, can be employed.

To achieve a good conductive interface 14 throughsemiconductor-to-semiconductor direct wafer bonding, it is usually, butnot always, required to perform a surface treatment step on at leastone, preferably both, of the wafers, before bonding to obtain eitherhydrophilic or hydrophobic surfaces.

Hydrophobic surfaces can be achieved, for example, by utilizing a HF dipprocess such as disclosed in S. Bengtsson, et al., “Interface chargecontrol of directly bonded silicon structures”, J. Appl. Phys. V 66, p1231, (1989), while hydrophilic surfaces can be achieved by either a dryclean process, such as, for example, an oxygen plasma (See, S. Farrens,“Chemical free room temperature wafer to wafer bonding”, J. Electrochem.Soc. Vol 142, p3949, (1995)); an argon high-energy beam surface etching,and/or a wet chemical oxidizing acid such as H₂SO₄ or HNO₃ solution. Thewet etching process is disclosed, for example, in M. Shimbo, etc.“Silicon-to-silicon direct bonding method”, J. Appl. Phys. V 60, p 2987(1986).

Although hydrophobic surfaces may provide better electronic properties,hydrophilic surfaces may provide sufficient conductivity because thenative oxide present at the bonding interface is usually only 2–5 nm.Moreover, substrates formed by the direct bonding of two hydrophilicsurfaces tend to have a large leakage current. Furthermore, crystallinejunctions can be formed after a high-temperature anneal step isperformed to further enhance the current flow across the bondinginterface 14.

Direct semiconductor-to-semiconductor wafer bonding (with or without thesurface treatments mentioned above) is achieved in the present inventionby first bringing the two wafers having different crystal orientationsinto intimate contact with other; optionally applying an external forceto the contacted wafers; and then optionally annealing the two contactedwafers under conditions that are capable of increasing the bondingenergy between the two wafers. The annealing step may be performed inthe presence or absence of an external force. Bonding is achievedtypically during the initial contact step at nominal room temperature.By nominal room temperature, it is meant a temperature from about 15° C.to about 40° C., with a temperature of about 25° C. being morepreferred.

After bonding, the wafers are typically annealed to enhance the bondingstrength and improve the interface property. The annealing temperatureis typically carried out at a temperature from about 900° to about 1300°C., with annealing temperature from about 1000° to about 1100° C. beingmore typical. Annealing is performed within the aforementionedtemperature ranges for various time periods that may range from about 1hour to about 24 hours. The annealing ambient can be O₂, N₂, Ar, or alow vacuum, with or without external adhesive forces. Mixtures of theaforementioned annealing ambients, with or without an inert gas, arealso contemplated herein.

Although high-temperature annealing (as described above) is often used,it is also possible to use a low temperature anneal (less than 900° C.)which can also achieve good mechanical and electrical properties.

It should be noted that the annealing step that follows the directsemiconductor-to-semiconductor bonding step can be performed at a singletemperature using a specific ramp-up rate, or it can be performed usingvarious temperatures in which various ramp-up rates and soak cycles areemployed.

To obtain a certain predetermined thickness of the second semiconductorlayer 16, various layer transfer techniques can be used in the presentinvention. One direct and simple approach that can be used in thepresent invention is to use wafer grinding, polishing or an etch backprocess. To provide better control of the layer transfer process, anetch stop layer 18 located between second semiconductor layer 16 and ahandling wafer 20 can be used (See FIG. 4A); the etch stop layer and thehandling wafer are both removed after wafer bonding. The etch stop layer18 can be an insulator, such as an oxide, nitride or oxynitride, whichmeans the starting top wafer may be an SOI substrate. Alternatively, theetch stop layer 18 can be another semiconductor material which can beremoved selectively from the second semiconductor layer 16 after bondingand also serve as an etch stop to remove the handling wafer 20.

Another layer transfer technique, applicable to embodiments where one ofthe wafers includes an ion implant region, is illustrated in FIG. 4B. Inthis case, the ion implant region 22 forms a porous region which causesa portion of the wafer above the ion implant region to break off leavinga bonded wafer such as is shown, for example, in FIG. 4B. The implantregion 22 is typically comprised of hydrogen ions that are implantedinto the surface of one of the wafers utilizing ion implantationconditions that are well known to those skilled in the art. Afterbonding, a heating step is typically performed in an inert ambient at atemperature from about 100° to about 400° C. for a time period fromabout 2 to about 30 hours to increase the bonding energy. Morepreferably, the heating is performed at a temperature from about 200° toabout 300° C. for a time period from about 2 to about 20 hours. The term“inert ambient” is used in the present invention to denote an atmospherein which an inert gas, such as He, Ar, N₂, Xe, Kr or a mixture thereof,is employed. A preferred ambient used during the bonding process is N₂.The layer splitting at the implant region 22 will take place during a350°–500° C. annealing afterwards.

The hybrid substrate 10 shown in FIG. 3 (which can be formed by avariety of layer transfer techniques) is used as the starting substratefor the method of the present invention that is depicted in FIGS. 5A–5E.The process flow depicted in these drawings will now be described ingreater detail.

After providing the hybrid substrate 10 shown in FIG. 3, a hard masklayer, i.e., pad stack, 24 is formed on an exposed upper surface of thesecond semiconductor layer 16 utilizing a deposition process such as,for example, chemical vapor deposition (CVD), plasma-enhanced chemicalvapor deposition (PECVD), chemical solution deposition, atomic layerdeposition, or physical vapor deposition. Alternatively, the hard masklayer 24 can be formed utilizing a thermal oxidation, nitridation oroxynitridation process. The resultant structure including the hard masklayer 24 is shown, for example, in FIG. 5A.

The hard mask layer 24 is composed of a dielectric material such as, forexample, an oxide, nitride, oxynitride or a stack thereof. The thicknessof the hard mask layer 24 may vary depending on the composition of themask material as well as the technique that was used in forming thesame. Typically, the hard mask layer 24 has, an as deposited thickness,from about 5 to about 500 nm.

The hard mask layer 24 is then patterned by lithography and etching toprovide a patterned mask 24′ such as shown, for example, in FIG. 5B. Thepatterned mask 24′ is used as an etch mask to remove an exposed portionof the second semiconductor layer 16 of the hybrid substrate 10,stopping either on an upper surface of the first semiconductor layer 12or within the first semiconductor layer 12. The resultant structureafter pattern transfer is shown, for example, in FIG. 5B. As shown, anopening 26 is provided in the hybrid structure that exposes theunderlying first semiconductor layer 12.

The etching of the hard mask layer 24 and pattern transfer may beperformed utilizing a single etching process or multiple etching stepsmay be employed. The etching may include a dry etching process such asreactive-ion etching, ion beam etching, plasma etching or laser etching,a wet etching process wherein a chemical etchant is employed or anycombination thereof. In one preferred embodiment of the presentinvention, reactive-ion etching (RIE) is used in selectively removingthe unprotected portions of the second semiconductor layer 16.

The opening 26 is used in defining different active device regions forthe subsequent formation of semiconductor devices. Consistent with theterminology used in the present application, the area that will includethe second semiconductor layer 16 as the active device layer will bereferred to herein as second device region 28, while the area that willinclude the first semiconductor layer 12 (as an epitaxial regrown layer,to be subsequently described) as the active device layer will bereferred to herein as first device region 30.

Next, an optional spacer 32 can be formed in the opening 26 on theexposed sidewalls provided by the above processing steps. The optionalspacer 32 is formed by deposition and etching. The optional spacer 32can be comprised of an insulating material such as, for example, anoxide, nitride, oxynitride or any combination thereof. The optionalspacer 32 may be a single spacer, as shown, or it may comprise multiplespacers. FIG. 5C shows the presence of optional spacers 32 in thestructure.

A semiconductor material 34 is then formed on the exposed surface of thefirst semiconductor layer 12 to provide the structure shown, forexample, in FIG. 5C. In accordance with the present invention,semiconductor material 34 has a crystallographic orientation that is thesame as the crystallographic orientation of the first semiconductorlayer 12. Although this regrown semiconductor layer will have the samesurface orientation as the first semiconductor layer 12, it can be of adifferent semiconductor material than the first semiconductor layer 12.

The semiconductor material 34 may comprise any semiconductor material,such as Si, strained Si, SiGe, SiC, SiGeC or combinations thereof, whichis capable of being formed utilizing a selective epitaxial growthmethod. Semiconductor material 34 can be strained, unstrained, or it canbe comprised of stained and unstrained layers, e.g., strained Si on arelaxed SiGe layer.

In some preferred embodiments, semiconductor material 34 is comprised ofSi. In other preferred embodiments, the semiconductor material 34 is astrained Si layer that may or may not be located atop a relaxed SiGealloy layer. In the present invention, semiconductor material 34 isreferred to as a regrown semiconductor material.

To achieve a high quality regrown semiconductor layer 34, selectiveepitaxy is recommended where there is no polysilicon or amorphoussilicon formed on top of the patterned mask 24′ outside the openings 26.To eliminate a facet formation during the epitaxy, the semiconductormaterial 34 can be grown, in some embodiments, higher than the patternedmask 24′ and then it is polished down to the patterned mask 24′.

In other embodiments, the regrown semiconductor material 34 may berecessed at this point of the present invention utilizing a time etchingprocess such as a timed RIE. One or more additional semiconductor layerscan be formed directly on top of the recessed surface. The semiconductormaterials formed would each have the same crystallographic orientationas that of the first semiconductor layer 12.

To achieve a coplanar surface, the semiconductor material 34 may need tobe etched back to the same level as the second semiconductor layer 16.This etching can be performed by dry etching, wet etching or oxidationof silicon and then stripping away the oxide.

The patterned mask 24′ is now removed from the structure utilizing aconventional stripping process that is capable of selectively removingthe patterned mask 24′ from the structure. The structure that is formedafter the patterned mask 24′ has been removed is shown, for example, inFIG. 5D. In this structure, the second semiconductor device surface,i.e., second semiconductor layer 16, is substantially coplanar to thefirst semiconductor device surface, i.e., the regrown semiconductormaterial 34.

After providing the structure shown in FIG. 5D, standard CMOS processingcan be performed, including, for example, device isolation formation,well region formation, and gate region formation. Specifically, afterproviding the structure shown, in FIG. 5D, isolation regions 36 (See,FIG. 5E), such as shallow trench isolation regions, are typically formedso as to isolate the first semiconductor active device region 30 fromthe second semiconductor active device region 28.

The isolation regions 36 are formed utilizing processing steps that arewell known to those skilled in the art including, for example, trenchdefinition and etching; optionally lining the trench with a diffusionbarrier; and filling the trench with a trench dielectric such as anoxide. After the trench fill, the structure may be planarized and anoptional densification process step may be performed to densify thetrench dielectric.

Next, well regions are formed into the exposed semiconductor devicelayers, i.e., layer 16 or regrown semiconductor material 34, byutilizing ion implantation and annealing, both of which are well knownto those skilled in the art. The well regions are designated byreference numeral 38 in FIG. 5E. The well regions may be n-type wellregions or p-type well regions depending on the type of semiconductordevice to be formed on each semiconductor layer, i.e., secondsemiconductor layer 16 and regrown semiconductor material 34. Forexample, if the semiconductor device is a pFET, well region 38 will bean n-type well, while if the semiconductor device is an nFET, wellregion 38 is a p-type well. Doping of each well is performed indifferent implant steps in which an implant mask is formed atoplocations in which the specific dopant is not intended to be implantedinto. The well regions 38 serves as body contacts in the presentapplication. The depth of the well regions 38 can vary depending on theimplant and annealing conditions as well as the type of dopant used.

After well formation, semiconductor devices, i.e., pFETs and nFETs, areformed on the exposed semiconductor layers, i.e., second semiconductorlayer 16 and regrown semiconductor material 34. Specifically, a secondsemiconductor device 50 is formed on a portion of the secondsemiconductor layer 16 and a first semiconductor device 52 is formed onthe regrown semiconductor material 34. Despite showing the presence ofonly one semiconductor device in each device region, the presentinvention contemplates forming a plurality of each type of device in thespecific device region. In accordance with the present invention, thefirst semiconductor device 52 may be a pFET or an NFET, whereas thesecond semiconductor device 50 may be an nFET or pFET, with the provisothat the first semiconductor device is different from the secondsemiconductor device and that the specific device is fabricating on acrystal orientation that provides a high performance device.

The pFETs and nFETs are formed utilizing standard CMOS processing stepsthat are well known to those skilled in the art. Each FET includes agate dielectric, a gate conductor, an optional hard mask located atopthe gate conductor, spacers located on sidewalls of at least the gateconductor, and source/drain diffusion regions. Note that the pFET isformed over the semiconductor material that has a (110) or (111)orientation, whereas the nFET is formed over a semiconductor surfacehaving a (100) or (111) orientation. The resultant structure includingbulk-like FETs is shown in FIG. 5E.

In the present invention, there are several ways to design the bulk-likenFETs and pFETs on the hybrid substrate with different crystalorientations. The main issue here is device and well isolation due tothe introduction of the interface 14. In the following examples, pFETsare located on (110) silicon and nFETs are located on (100) silicon witha traditional p-type substrate. The STI depth should be designed to havetradition isolation between nFET-pFET, nFET-nFET and pFET-pFET.

In FIGS. 6–7, there is shown that the conductive (i.e., bonding)interface 14 can be designed to be below the isolation regions 36 andthe wells 38. In case of (110) Si 16 on top of (100) Si 12 (as shown inFIG. 6), nFETs in p-well are on the (100) epi-layer 34 and the pFETs inn-well are on (110) Si 16. To avoid well-to-well leakage, the interface14 should be below the n-well. Specifically, it should be outside thedepletion region of the well pn junctions. The depletion width of a pnjunction is reverse proportional to their doping level. The p-well top-well connection is from the epi layer through the first semiconductorand/or across the bonding interface/epitaxy interface. Devices in thesame well can share the same well contact (to avoid floating body). Inthis specific scenario, the conductivity of the bonding interface is notcritical, i.e., the bonding interface can be insulator and the bondingcan be Si-to-Si, Si-to-oxide or oxide-to-oxide bonding. However, aconducting bonding interface is preferred.

In case of (100) Si 16 on top of (110) Si 12 (as shown in FIG. 7), pFETsin n-well are on (110) epi-layer 34 and nFETs in p-well are on (100) Si16. To avoid well-to-well leakage, the bonding interface still should beaway from the well pn junctions, thus the top Si thickness 16 will besimilar to the case in FIG. 6. In this case, p-well to p-well connectionwill go across the bonding interface and/or the epitaxy interface.Although the conductivity of the bonding interface is not critical,i.e., the bonding interface can be insulator, a good conduction bondinginterface is preferred by using Si-to-Si direct bonding as describedabove.

In FIGS. 8–9, there is shown that the bonding interface can be designedinside the well but below isolation region 36 as long as the spacerformed before the epitaxy provides good isolation to the end of theprocess, where it acts as additional isolation between the wells. Incase of (110) Si 16 on top of a (100) handle wafer 12 (as shown in FIG.8), pFETs in n-well are on (110) Si 16 and nFETs in p-well are on (100)epi-Si 34. The bonding interface can be above the well junctions as longas it is far enough from the well pn junction depletion region. Thespacer (and the stack etch) should also be below the bonding interfaceto clear off the well junctions from the bonding interface on the side.In this case, p-well to p-well connections will go from epi-Si throughthe handle wafer. However, devices in the same n-well will be connectedthrough underneath the STI with or without crossing bonding interface.It is preferred that the bonding interface can have good conductivity toensure every pFET in the same n-well has good body contact. In case(100) Si 16 on top of (110) Si 12 (as shown in FIG. 9), the bondinginterface is inside the p-well. The only requirement is that the spacer(and the stack etch) should be below the bonding interface to clear offthe well pn junction on the side. In this scenario, p-well to p-wellconnection has to go across the bonding interface. Moreover to ensuregood the body contact of every nFETs in the same p-well, goodconductivity of the bonding interface is required.

In FIGS. 10–11, there is shown how that the bonding interface can bedesigned above the STI. In case of (110) Si 16 on top of (100) handle 12wafer (FIG. 10), both the bonding interface and well junction are belowpFETs. To avoid S/D leakage, the bonding interface should be below thesource/drain junction depletion depth. To avoid well-to-well leakage,the bonding interface should be also outside the well junction depletionregion. Furthermore, the STI should be deep enough to clear off the welljunction from the bonding interface on the side. To avoid floating bodyfor the pFETs, the bonding interface is required to give goodconductivity.

In case of (100) Si on (110) handle (as shown in FIG. 11), it is similarto the case in FIG. 10. To avoid S/D leakage, the bonding interfaceshould be below the source/drain junction depletion depth. However,since the bonding interface is in p-well, to avoid well-well leakage,the STI depth is the only requirement for well isolation. To avoidfloating body for the nFETs and have connections between p-well top-well, the bonding interface is required to give good conductivity.

The above-described bulk-like CMOS on hybrid substrate can also becombined with strained Si process (See FIGS. 12–16). It is known that annFET on (100) strained Si layer has higher performance than that onunstrained (100) Si substrate. Also it is known that a pFET on (110)strained Si layer has higher performance than that on unstrained (110)Si substrate. The strained Si layer is achieved by growing a relaxedSiGe buffer on either the top Si or the bottom Si.

The strained Si processes contemplated by the present invention will bedescribed with reference to the specific embodiments shown in FIGS.12–16. Unless otherwise specified, the processing steps and materialsused above are used in the strained Si embodiments.

FIGS. 12A–12D show an embodiment for providing strained Si MOSFETdevices. In FIG. 12A, there is shown hybrid structure 10 that includesfirst semiconductor layer 12, interface 14, and second semiconductorlayer 16 that is formed as described above.

Next, and as shown in FIG. 12B, a relaxed buffer layer 70 such as SiGehaving the same crystallographic orientation as the second semiconductorlayer 16 is formed by epitaxy. After formation of the relaxed bufferlayer 70, a strained semiconductor layer 72, such as strained Si, isdeposited on the relaxed buffer layer 70. In this embodiment of thepresent invention, the strained/relaxed layers have the samecrystallographic orientation as the second semiconductor layer 16.

A masking layer (hereinafter referred to as a “pad stack”) comprising apad oxide 74 and a pad nitride 76 are then formed by deposition and thepad stack is subjected to lithography and etching so as to expose aportion of the second semiconductor layer 16. The exposed portion of thesecond semiconductor layer 16 is then etched stopping on, or within, thefirst semiconductor layer 12. Optional spacer 32 are then formed on eachsidewall within the opening provided by the aforementioned etching step.The resultant structure is shown, for example, in FIG. 12C.

FIG. 12D shows the structure after semiconductor material 34 is regrownfrom the exposed surface of first semiconductor layer 12 and afterplanarization. The pad oxide 74 and nitride 76 may now be removed andCMOS devices as described above can be formed on the strained Si layer72 and the regrown semiconductor material 34.

FIGS. 13A–13D show another embodiment that can be employed in thepresent invention. In this embodiment, the relaxed buffer layer 70 andstrained semiconductor 72 are formed in the opening on the exposedsurface of the first semiconductor layer 12. In this instance, therelaxed buffer layer/strained semiconductor stack has the samecrystallographic orientation as the first semiconductor layer 12. Theprocessing steps used in this embodiment are similar to those describedabove in connection with FIGS. 12A–12D except for the location of therelaxed buffer layer and the strained semiconductor layer.

FIGS. 14A–14D shows another embodiment of the present invention. In thisembodiment, a semiconductor wafer, as shown in FIG. 14A, is employed asone of the wafers for direct bonding. In particular, the wafer shown inFIG. 14A includes a relaxed semiconductor layer 12′, such as SiGe, thatis formed on a handling wafer 80. Relaxed semiconductor layer 12′ hasthe same characteristics as first semiconductor layer 12 describedabove. Next, a second semiconductor layer 16 having a different crystalorientation than the relaxed semiconductor layer 12′ is bonded to thewafer shown in FIG. 14A using the direct bonding technique mentionedabove to provide the structure shown in FIG. 14B.

A patterned pad stack comprising pad oxide 74 and pad nitride 76 is thenformed as described above, an opening is provided that exposes a portionof the relaxed buffer layer 12′, optional spacers 32 are formed and thena semiconductor material 34 is grown and planarized providing thestructure shown in FIG. 14C.

The semiconductor material 34 is then recessed using a timed etchingprocess. Strained semiconductor layer 72 is then formed on the recessedsemiconductor material 34 and thereafter the pad stack is removedproviding the structure shown in FIG. 14D. CMOS devices, as describedabove, are then formed on the second semiconductor layer 16 and thestrained Si layer 72. Note that the strained Si layer 72 has the samecrystallographic orientation as the relaxed buffer layer 12′ which isdifferent from the second semiconductor layer 16.

FIGS. 15A–15D show a further embodiment of the present invention. Inthis embodiment, a first semiconductor layer 12 is directly bonded to asecond semiconductor layer 16. A relaxed semiconductor 70 and a strainedsemiconductor layer 72 are then formed (as described above) on thesecond semiconductor layer 16 providing the structure shown in FIG. 15B.

A pad stack comprising pad oxide 74 and pad nitride 76 are then formedon the strained semiconductor layer and thereafter patterned. An openingextending down to the first semiconductor layer 12 is provided and thenoptional spacers 32 are formed in the opening. After optional spacer 32formation, a semiconductor material 34 comprising a relaxed SiGe layeris formed and planarized providing the structure shown, for example inFIG. 15C. A portion of the relaxed SiGe layer 34 is recessed utilizing atime reactive ion etch process and thereafter strained semiconductorlayer 72′ is provided and the pad stack is removed from the structureproviding the structure shown in FIG. 15D. In this case, the strainedsemiconductor layer 72 has a different crystallographic orientation ascompared to strained semiconductor layer 72′. CMOS device can be formedon each of the strained semiconductor layers as described above.

FIGS. 16A–16B show a still further embodiment of the present invention.In this embodiment, a relaxed semiconductor layer 12′ is formed on ahandling wafer 80 (See, FIG. 16A) and then that semiconductor layer isdirectly bonded to a second semiconductor layer 16. A relaxed bufferlayer 70 and a strained semiconductor layer 72 having the samecrystallographic orientation as that of the second semiconductor layer16 is then formed and a pad stack comprising pad oxide 74 and padnitride 74 is provided. After lithography and etching which exposes asurface portion of the relaxed semiconductor layer 12′, optional spacers32 are formed and a relaxed semiconductor layer 34 is epitaxial grown onthe relaxed semiconductor layer 12′ and then the structure isplanarized. FIG. 16C shows the resultant structure.

The regrown relaxed semiconductor layer 34 is recessed as describedabove and a stained Si layer 72′ is formed on the recessed surface. Thestructure is then planarized providing the structure shown in FIG. 16D.CMOS devices are then formed, as described above, on strainedsemiconductor layer 72 and strained semiconductor layer 72′. Inaccordance with the present invention, each of the strainedsemiconductor layers has different crystallographic orientation.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A hybrid substrate comprising: a first semiconductor layer having afirst crystallographic orientation; and a second semiconductor layerhaving a second crystallographic orientation which is different from thefirst crystallographic orientation, wherein said first and secondsemiconductor layers are separated from each other by a conductiveinterface that has an upper surface that is in contact with said secondsemiconductor layer and a lower surface that is in contact with saidfirst semiconductor layer, said conductive interface comprises ahydrophilic surface or a hydrophobic surface of at least one of saidsemiconductor layers.
 2. The hybrid substrate of claim 1 wherein saidfirst semiconductor layer and the second semiconductor layer arecomposed of the same or different semiconductor material selected fromthe group consisting of Si, SiC, SiGe, SiGeC, Ge, GaAs, InAs, InP, otherIII/V or II/VI compound semiconductors and any combination thereof. 3.The hybrid substrate of claim 1 wherein said first semiconductor layerand the second semiconductor layer are both composed of Si.
 4. Thehybrid substrate of claim 1 wherein said first semiconductor layer has a(100) crystal orientation and said second semiconductor layer has a(110) crystal orientation.
 5. The hybrid substrate of claim 1 whereinsaid first semiconductor layer has a (110) crystal orientation and saidsecond semiconductor layer has a (100) crystal orientation.
 6. Thehybrid substrate of claim 1 wherein said first semiconductor layercomprises a relaxed semiconductor material or a stack of a relaxedsemiconductor material and a strained semiconductor material.
 7. Thehybrid substrate of claim 1 wherein said second semiconductor materialcomprises a relaxed semiconductor material or a stack of a relaxedsemiconductor material and a strained semiconductor material.
 8. Anintegrated semiconductor structure comprising: a hybrid structurecomprising a first device region having a first crystallographicorientation and a second device region having a second crystallographicorientation, said first crystallographic orientation is different fromsaid second crystallographic orientation, and wherein said hybridstructure comprises a hybrid substrate that comprises a firstsemiconductor layer having said first crystallographic orientation and asecond semiconductor layer having said second crystallographicorientation, said first and second semiconductor layers are separatedfrom each other by a conductive interface; an isolation regionseparating said first device region from said second device region; andat least one first semiconductor device located in said first deviceregion and at least one second semiconductor device located in saidsecond device region, wherein said first semiconductor device and saidsecond semiconductor device are both bulk-like devices and both devicescontain a well region that serves as a body contact.
 9. The integratedsemiconductor structure of claim 8 wherein the first crystallographicorientation is (110) and the second crystallographic orientation is(100).
 10. The integrated semiconductor structure of claim 9 whereinsaid at least one first semiconductor device is a pFET and the at leastone second semiconductor device is an nFET.
 11. The integratedsemiconductor structure of claim 8 wherein the first crystallographicorientation is (100) and the second crystallographic orientation is(110).
 12. The integrated semiconductor structure of claim 11 whereinsaid at least one first semiconductor device is an nFET and the at leastone second semiconductor device is a pFET.
 13. The integratedsemiconductor structure of claim 8 wherein the first device regionincludes a regrown semiconductor material located atop a firstsemiconductor material, said regrown semiconductor material having thesame crystallographic orientation as the first semiconductor material.14. The integrated semiconductor structure of claim 13 wherein saidregrown semiconductor material is recessed and another semiconductormaterial is formed atop the recessed regrown semiconductor material. 15.The integrated semiconductor structure of claim 14 wherein said anothersemiconductor material is a strained semiconductor or a stack comprisinga relaxed semiconductor and a strained semiconductor.
 16. The integratedsemiconductor structure of claim 13 wherein said regrown semiconductormaterial is a semiconductor selected from the group consisting of Si,SiC, SiGe, SiGeC, Ge, GaAs, InAs, InP, other III/V or II/VI compoundsemiconductors and any combination thereof.
 17. The integratedsemiconductor structure of claim 8 wherein said first and secondsemiconductor device regions both include strained Si.
 18. Theintegrated semiconductor structure of claim 13 wherein said regrownsemiconductor material comprises a strained semiconductor layer locatedatop a relaxed semiconductor layer.